Certain unsymmetrical dialkyl-p-phenylenediamines are known. For example, certain unsymmetrical dialkyl-p-phenylenediamines in which one alkyl is derived from an aldehyde and the other from a ketone are described in U.S. Pat. No. 3,504,032 and test results described which indicate that they possess antidegradant activity for diene elastomers comparable to that of the symmetrical N,N'-di(sec-alkyl)-p-phenylenediamines having 7 or 8 carbon atoms in each alkyl group which have become widely accepted in the rubber industry. However, reaction with aldehydes is difficult to control and leads to excessive by-product formation. Moreover, the requirements of low volatility and high degree of safety to workmen coming in contact with either the antidegradant or preserved rubber are severely limiting of practically usable antidegradants.